This invention relates to priority interrupt apparatus and to methods for handling priority interrupt requests in a digital data processing system or digital computer system.
The rapid handling of interrupt requests from different interrupt sources plays an important part in digital data processing systems, particularly in those systems employed in real time applications. In a process control application, for example, a plurality of interrupt sources, such as sensors for temperature, pressure, moisture, flow rate and the like, necessitate interruptions or changes of the control process or operating sequence and it is essential that interrupt requests from such sources are handled very quickly.
Some previous solutions for handling interrupt requests have been based on very expensive data processing hardware mechanisms with complicated circuit structures which, although reacting at the required speed, are elaborate and prone to defects because of their complicated structure.
An alternative solution frequently adopted in the past involves the use of various software programs and structures stored in the data processing system for providing the desired priority level switching. Although this software approach is less elaborate and somewhat more reliable than the complicated hardware approach, it is, nevertheless, too slow for a goodly number of applications.